A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m s - 1 . Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air = 330 m s - 1 )

Question

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m s - 1 . Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air = 330 m s - 1 ), 765 Hz, 800 Hz, 838 Hz, 885 Hz

MARKS App · Accepted Answer

Given here, f o = 800 H z V s = 15 m s - 1 Using Doppler's effect, the frequency of sound that the observer hears in the echo reflected from the cliff is f a = f o V + V o V − V s ⇒ f a = 330 330 - 15 × 800 = 330 315 × 800 f a = 838 H z

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